The present invention relates to a sintered ceramic body which mainly consists of silicon nitride.
Recently, ceramics have frequently been used for engine parts or the like.
Such a ceramic part is obtained by forming a ceramic into a predetermined shape and sintering the formed ceramic body, or cutting a sintered ceramic body into a predetermined shape.
However, a sintered ceramic body of a complex shape such as a turbine rotor has low local mechanical strength and variations in its overall mechanical strength. This is considered to be attributable to the following reason. Since a part having a complex shape is difficult to form by press forming it is therefore manufactured by cutting or grinding a formed, sintered ceramic body. Thus, the resultant part has both a cut or ground surface and a non-cut or non-ground surface (sintered surface).
According to experiments conducted by the present inventors, it was found out that the mechanical strength of a sintered surface is about 40 to 70% that of a cut or ground surface. It was also found out that the sintered surface has great variations in mechanical strength and lacks uniformity. For this reason, a part having a partially sintered surface is considered to have variations in mechanical strength, thus impairing various properties of the part.